Although aerosolized pentamidine is effective in limiting the occurrence of Pneumocystis carinii (PC) pneumonia, its use may actually be associated with preferentially manifested upper lobe pneumonia due to PC. This may be a function of the pattern of lung distribution of pentamidine by the conventional (Respirgard II) nebulizer. In this pilot study, tolerance of a new nebulizer (Babington model) will be assessed and compared with the conventional nebulizer. In addition, there will be an attempt to quantify pentamidine distribution geographically, using nuclear medicine scanning techniques and, chemically, using bronchoalveolar lavage analysis. The goal of this prospective study is to determine the mode of nebulization that most effectively allows for equal pulmonary distribution of the drug, and, in doing so, is best tolerated by the patient. Efficacy is not being addressed in this study.